The purposes of this study are to define the localization of iron accumulation within the copper-deficient liver and to define the nature of the accumulated iron substance. Iron accumulates with all subcellular compartments except the nuclear fraction. Further studies will examine iron distribution within the various constituents of this fraction as well as distribution within the components of other organelles. These studies may provide insight into the means by which iron is transported within the cell. Accumulated iron has been obtained from hepatic homogenates from copper deficient rats. Studies will be directed toward purification and characterization of the iron substance using standard protein purification techniques. In addition, the role of this substance as substrate for mitochondrial heme synthesis will be evaluated. Calcium, calcium ionophores and metabolic inhibitors will be evaluated in experiments measuring iron utilization from the iron substance for heme synthesis, measured by the heme chromogen method. If there is homology between calcium and iron utilization by mitochondria, attempts will be made to identify additional iron-carrier protein.